Methyl Salicylate, also know as Oil of Wintergreen is a minty smelling oil naturally produced by wintergreen trees. It is used in many ointments used to treat joint pain. Today we will be making it artificially using methanol and salicylic acid. This is a fischer esterification reaction.
Materials:
- 2 beakers
- 50.00 grams of salicylic acid
- 40ml of concentrated sulphuric acid
- 250ml of methanol
- 100ml graduated cylinder
- Hotplate
- Electronic mass balance
- 500ml three-neck round bottom flask (RBF)
- 50ml one-neck round bottom flask (RBF)
- 150mm evaporating dish
- 250ml separatory funnel
- 200ml ice cold water
- 200ml saturated sodium bicarbonate solution
- 300mm Allihn condenser
Procedure:
- Weigh out 50g of salicylic acid and add to the RBF.
- Measure out 250ml of methanol and add the methanol to the RBF containing salicylic acid.
- Mix until all of the salicylic acid has been dissolved.
- Measure out 40ml of concentrated sulfuric acid with the graduated cylinder.
- Add the sulfuric acid slowly and with a lot of stirring to the RBF. Be careful and add it slowly because the dissolution of sulphuric acid in methanol is very exothermic and if too much is added too quickly it may cause uncontrollable boiling. My mixture turned purple because of iron contamination in my drain cleaner grade sulphuric acid. If you use reagent grade this should not happen.
- Set up a reflux apparatus with a condenser and reflux for 1.5 hours.
- After refluxing for 1.5 hours, dismantle the reflux and pour the contents into the evaporating dish.
- Set the evaporating dish on the hotplate set at 55C and evaporate off half the volume of methanol.
- At this point you should see two layers forming, transfer it to the separatory funnel.
- Add 200ml of ice cold water to the separatory funnel, cap and shake. Let it stand for a few minutes.
- Drain the bottom layer of crude methyl salicylate into a beaker. Discard the upper aqueous layer.
- Transfer the methyl salicylate back into the separatory funnel, then wash with 100ml of saturated sodium bicarbonate solution. Repeat with another 100ml of saturated sodium bicarbonate.
- Transfer the crude methyl salicylate into a 50ml RBF and set up for simple distillation. Be careful if using plastic keck clips as methyl salicylate boils at 220 degrees celsius and plastic clips can melt.
- Distill the methyl salicylate until no more liquid remains in the distillation flask.
I ended up with about 30ml of completely clear methyl salicylate which is about a 65% yield. The oil smells very much like Listerine. However, you should not eat it because it is toxic and an amount as low as 5ml can cause death.
*Procedure taken and adapted from Nile Red's video on Youtube:
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